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  <h1>
  Notes on the ctype implementation.
  </h1>
<em>
prepared by Benjamin Kosnik (bkoz@redhat.com) on August 30, 2000
</em>

<h2>
1. Abstract
</h2>
<p>
Woe is me.
</p>

<h2>
2. What the standard says
</h2>


<h2>
3. Problems with &quot;C&quot; ctype : global locales, termination.
</h2>

<p>
For the required specialization codecvt&lt;wchar_t, char, mbstate_t&gt; ,
conversions are made between the internal character set (always UCS4
on GNU/Linux) and whatever the currently selected locale for the
LC_CTYPE category implements.
</p>

<h2>
4. Design
</h2>
The two required specializations are implemented as follows:

<p>
<code>
ctype&lt;char&gt;
</code>
</p>
<p>
This is simple specialization. Implementing this was a piece of cake.
</p>

<p>
<code>
ctype&lt;wchar_t&gt;
</code>
</p>
<p>
This specialization, by specifying all the template parameters, pretty
much ties the hands of implementors. As such, the implementation is
straightforward, involving mcsrtombs for the conversions between char
to wchar_t and wcsrtombs for conversions between wchar_t and char.
</p>

<p>
Neither of these two required specializations deals with Unicode
characters. As such, libstdc++-v3 implements 
</p>

<h2>
5.  Examples
</h2>

<pre>
  typedef ctype&lt;char&gt; cctype;
</pre>

More information can be found in the following testcases:
<ul>
<li> testsuite/22_locale/ctype_char_members.cc    </li>
<li> testsuite/22_locale/ctype_wchar_t_members.cc </li>
</ul>

<h2>
6.  Unresolved Issues
</h2>

<ul>
   <li> how to deal with the global locale issue? </li>

   <li> how to deal with different types than char, wchar_t? </li>

   <li> codecvt/ctype overlap: narrow/widen </li>

   <li> mask typedef in codecvt_base, argument types in codecvt.
   what is know about this type? </li>

   <li> why mask* argument in codecvt? </li>
   
   <li> can this be made (more) generic? is there a simple way to
   straighten out the configure-time mess that is a by-product of
   this class? </li>

   <li> get the ctype&lt;wchar_t&gt;::mask stuff under control. Need to
   make some kind of static table, and not do lookup evertime
   somebody hits the do_is... functions. Too bad we can't just
   redefine mask for ctype&lt;wchar_t&gt; </li>
   
   <li> rename abstract base class. See if just smash-overriding
   is a better approach. Clarify, add sanity to naming. </li>

</ul>


<h2>
7. Acknowledgments
</h2>
Ulrich Drepper for patient answering of late-night questions, skeletal
examples, and C language expertise.

<h2>
8. Bibliography / Referenced Documents
</h2>

Drepper, Ulrich, GNU libc (glibc) 2.2 manual. In particular, Chapters &quot;6. Character Set Handling&quot; and &quot;7 Locales and Internationalization&quot;

<p>
Drepper, Ulrich, Numerous, late-night email correspondence
</p>

<p>
ISO/IEC 14882:1998 Programming languages - C++
</p>

<p>
ISO/IEC 9899:1999 Programming languages - C
</p>

<p>
Langer, Angelika and Klaus Kreft, Standard C++ IOStreams and Locales, Advanced Programmer's Guide and Reference, Addison Wesley Longman, Inc. 2000
</p>

<p>
Stroustrup, Bjarne, Appendix D, The C++ Programming Language, Special Edition, Addison Wesley, Inc. 2000
</p>

<p>
System Interface Definitions, Issue 6 (IEEE Std. 1003.1-200x)
The Open Group/The Institute of Electrical and Electronics Engineers, Inc.
http://www.opennc.org/austin/docreg.html
</p>

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